1. Field of the Invention
The present invention generally relates to the field of DC power supplies. More specifically, the present invention relates to a technique for selecting voltage output reference of a DC-DC converter included in a computer system in response to an operating state of the computer system.
2. Description of the Related Art
Information systems in general have attained widespread use in business as well as personal computing environments. An information handling system, as referred to herein, may be defined as an instrumentality or aggregate of instrumentalities primarily designed to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle or utilize any form of information, intelligence or data for business, scientific, control or other purposes. The information handling system may be configured for a specific user application or requirement such as financial transaction processing, airline reservations, enterprise data storage and/or global communications. In general, an information handling system may include a variety of hardware and/or software components that may be configured to provide information and/or consume information. An information handling system may include one or more computer systems, data storage systems, and/or networking systems.
A computer system, which is one common type of information handling system, may be designed to give independent computing power to one or a plurality of users. Computer systems may be found in many forms including, for example, mainframes, minicomputers, workstations, servers, clients, personal computers, Internet terminals, notebooks, personal digital assistants, and embedded systems.
A computer system may be available as a desktop, floor-standing unit, or as a portable unit. The computer system typically includes a microcomputer unit having a processor, volatile and/or non-volatile memory, a display monitor, a keyboard, one or more floppy diskette drives, a hard disc storage device, an optional optical drive, e.g., DVD, CD-R, CD-RW, Combination DVD/CD-RW or CD-ROM, and an optional printer. A computer system also includes an operating system, such as Microsoft Windows XP™ or Linux. A computer system may also include one or a plurality of peripheral devices such as input/output (“I/O”) devices coupled to the system processor to perform specialized functions. Examples of I/O devices include keyboard interfaces with keyboard controllers, floppy diskette drive controllers, modems, sound and video devices, specialized communication devices, and even other computer systems communicating with each other via a network. These PO devices are typically plugged into connectors of computer system I/O interfaces such as serial interfaces and parallel interfaces, for example. Generally, these computer systems use a system board or motherboard to electrically interconnect these devices.
Typically, information handling systems are powered by a power supply system that receives and converts alternating current (“AC”) power to direct current (“DC”) power that is used to power the information handling system components such as the system processor. In one type of AC-DC power supply used to supply current at DC voltages, power is converted from an AC power source, such as 120 V, 60 Hz or 220 V, 50 Hz power, from a wall outlet. This is accomplished by first rectifying the AC voltage of the power source to an unregulated DC voltage. The unregulated DC voltage typically has a ripple waveform component. To “smooth” the ripple component, most power supplies incorporate a bulk filter capacitor or bulk reservoir capacitor. Typically, a bulk filter capacitor stores charge during the ripple peaks and releases charge during the low portion of the ripple cycle. In addition, AC-DC power supplies may typically include a DC-DC converter for providing DC power to the computer system within specified tolerances.
Typical DC-DC converters incorporate a switching circuit, a controller circuit, resistors, and diodes, in combination with a single-stage LC filter. The typical switching power supply is described in further detail in the text “Switching Power Supply Design”, Abraham I. Pressman, Second Edition, published by McGraw Hill, ISDN 0-07052236-7.
Advances in processor technology have consistently driven down the supply voltages required to operate processors, thereby reducing power consumption. The supply voltage for processors, which is presently in the +1.0 V to +2.5 V range, may soon extend below 1.0 V. The newer processors, such as Intel's Pentium class of processors, typically specify a profile or load line that defines the relationship between the processor supply voltage and the current drawn by the processor. For example, Application Note AP-587, “Slot 1 Processor Power Distribution Guidelines”, August 1998, Order Number: 243332-002, published by Intel Corporation describes the power requirements. It is quite common for processor manufacturers to make frequent changes to the supply voltages required by the processor. The dynamic voltage requirements can be a challenge, especially when extensive changes to the printed circuit boards are often required to accommodate the changes.
Present processor designs typically support a plurality of power operating states. For example, the Advanced Configuration and Power Interface (ACPI) specification, Revision 2.0, Jul. 27, 2000, published by Compaq Computer Corporation, Intel Corporation, Microsoft Corporation, Phoenix Technologies Ltd., and Toshiba Corporation typically defines various processor power states such as C0, C1, C2, C3, and C4. The Processor manufacturers typically require that transitions between these power operating states take place very rapidly, e.g., in less than 100 μs. To control the voltage output reference of the DC-DC converter, traditional methods and systems have relied on using multiplexers external to DC-DC controller. The use of multiplexers consumes valuable printed circuit board space and adds to the cost. Furthermore, in some cases the suspend, or startup, state voltage of the processor is selected by tying the DC-DC controller startup voltage state select pins to VCC,
REF and/or GND depending on the controller used. When the processor specification regarding the voltage required may necessitate a redesign of the printed board to support the new voltage. Present practice is to add resistor-strapping options to the DC-DC controller startup state pins to allow support of all possible startup state voltages. However, this option also results in the consumption of additional board space and typically results in a higher cost.
Present processors used in information handling systems have a feature called voltage identification (“VID”) which allows the processor to program the motherboard's power management system, e.g., a voltage regulator module (“VRM”), to deliver the proper voltage to the processor. The VID input to the power management system is typically a 5-bit digital signal, e.g., VIDO-4. Newer versions of the VID input may use additional bits, e.g., VIDO-5. Some DC-DC controllers, included in the power management system, have impedance-type selection pins at their voltage identification input that can source or sink current determining setting, by sampling voltage or impedance of the external resistor/capacitor networks. This design typically requires the use of unique board ID's or part numbers, thereby limiting support of various processors with different voltage state requirements. One example of a DC-DC controller is the Maxim MAX1718 controller from Maxim Integrated Products, Sunnyvale, Calif. The MAX1718 controller provides impedance-type selection pins at their voltage identification input and/or supports resistor strapping options.
What is needed is a DC-DC controller that effects rapid switchover between the allowable processor power operating state voltages. The voltages required by the processor are preferably configurable, without requiring the addition of a separate multiplexer and/or resistor-strapping option. Eliminating the need for separate components such as resistors also accomplishes an objective of reducing printed circuit board space.